Overload tripping devices for electric motor starting switches

ABSTRACT

A thermal tripping device for protecting three-phase electric motors against balanced sustained overloads in each phase and against unbalanced overloads, which comprises a quick make and break overcenter spring actuated by a bellcrank connecting slidable trip bars operated by thermal overload elements in each phase. An adjustable reset plunger has a cam formation for enabling hand or automatic reset of the trip mechanism.

United States Patent Theme [54] OVERLOAD TRIPPING DEVICES FOR ELECTRIC MOTOR STARTING SWITCHES [72] Inventor: Arthur Robert Hamilton Thorne, Solihull,

England [73] Assignee: J. A. Crabtree & Co., Limited, Walsall,

England [22] Filed: Nov. 20, 1969 [21] Appl. No.: 878,389

[52] U.S. Cl ..337/49, 337/95, 337/101 [51] Int. Cl. ..H0lh 37/30, l-IOlh 61/00, HOlh 73/30 [58] Field ofSearch ..337/37, 38,39,40, 49, 59, 337/62, 95, 101, 102, 335, 336

[5 6] References Cited UNlTED STATES PATENTS 3,475,709 10/1969 Basse ..337/49X 451 Jan. 25, 1972 3,257,526 6/1966 Ramsey et al.... ..337/38 3,015,007 12/1961 Howard ..337/62 FOREIGN PATENTS OR APPLICATIONS 1,043,750 7/1958 Germany ..337/39 1,199,868 9/1965 Germany ..337/49 Primary ExaminerBernard A. Gilheany Assistant Examiner- Dewitt M. Morgan Attorney-Lucke & Lucke 57 ABSTRACT A thermal tripping device for protecting three-phase electric motors against balanced sustained overloads in each phase and against unbalanced overloads, which comprises a quick make and break overcenter spring actuated by a bellcrank connecting slidable trip bars operated by thermal overload elements in each phase. An adjustable reset plunger has a cam formation for enabling hand or automatic reset of the trip mechanism.

5 Claims, 8 Drawing Figures PATENTEU JANZS I972 SHE" m? s PATENTED JANZS I972 SHEET 311? 5 PATENTED mes-m2 3638158 saw @141? 5' f a z 2 gvenlorg PATENTED M25 I972 SHEEY 50F 5 Home y 3 ,63 8 1 8 1 2 OVERLOAD TRIPPING DEVICES FOR ELECTRIC blade is a short helical compression spring 21 urging the other MOTOR STARTING SWITCHES This invention relates to improvements in and connected I with overload tripping devices for motor starters, and is particularly concerned with devices operated by thermally sensitive elements in the event of overload in the windings of a three-phase motor, such elements being uniformly distorted or flexed to actuate trip mechanism after a predetermined interval on the occurrence of a balanced and sustained overload in each of the protected phases, while causing the mechanism to be tripped and open the circuit without a time interval of this order in the event of an unbalanced overload or the condition known as single phasing.

The object of the present invention is to incorporate in the mechanism, simple mechanical adjustments to ensure reliably efficient operation with components, produced and assembled in economical manner by mass production methods, whereby production tolerances, the result of such methods, can be compensated for by the adjustments.

According to this invention the mechanism comprises a quick make and break overcenter spring actuated by a bellcrank connecting slidable trip members operated by thermal bimetal overload elements in each phase of the motor and adapted for effectively tripping on balanced or unbalanced overloads, an adjustable reset plunger having a peripheral cam adapted to be rotated for enabling hand or automatic reset of the trip mechanism, and mechanically adjustable setting means for the switch and bellcrank.

Assembly of parts is preferably carried out in jigs for accurately positioning the adjustable contacts. The improved arrangement avoids electrical joints and thereby provides greater efficiency.

In order to enable the invention to be readily understood reference will now be made to the accompanying drawings illustrating one example of construction for carrying the invention into effect, in which drawings:

FIG. I is an inverted plan to an enlarged scale.

FIG. 2 is an end elevation looking from the upper end of FIG. 1.

FIG. 3 is a section on the line III-III ofFIG. 1.

FIG. 4 is a side elevation of FIG. 1 with the small cover 42 removed.

FIG. Sis a section on the line V-V of FIG. 1.

FIGS. 6 and 7 are sections on the lines VI- VI respectively of FIG. 5.

FIG. 8 is a section on the line VIII-VIII of FIG. 1.

The construction comprises the usual three overload elements A and trip mechanism B housed in transverse compartments of a box 12 molded from insulating material. Each overload element A comprises a straight bimetal strip 15 disposed within a coiled heater wire 16, its free reduced end 15 protruding into slots in a pair of flat trip plates 7, 8, of insulating material. The plates 7, 8, are guidingly supported side by side by the partitions 17 of the box and their ends extend into a trip chamber 18. A link member in the form of a bellcrank 6 has one end pivotally connected at 6" to the plate 7, and a second end is pivotally connected at 6 to the plate 8. A forwardly extending hook-shaped formation 6" on the bellcrank 6 actuates the trip mechanism B. The trip plate 7 has an extension which is adapted to be projected into abutment with a flat bimetal blade 19, providing for ambient temperature compensation.

A rise in ambient temperature causesthe lower ends of all bimetals l5 and the ambient blade 19 to move to the right. At high temperature a stud or projection 19 riveted to the blade 19 abuts against the molded casing to prevent its further movement. Further movement of the bimetals 15 then causes the plate 7 to engage the blade 19 and produce trip actuation of the switch as hereinbefore described through movement of the plate 8 and the bellcrank 6. Such arrangement ensures that if the ambient temperature exceeds that for which the overload is designed there would be a safe failure.

The flat ambient blade 19 is pivoted at one end on a pin 20 extending from the casing, between the wall of which and the and VII-VII end of the blade away from the end of the trip bars. On the external wall of the casing is a flat adjusting lever 22, FIG. 4, pivoted on a rivet 23 and slotted for engaging the pin 24 of a pivotal sheet metal bracket 25 embracing the casing wall and having a guiding tooth 27 entering an elongated slot 26 in the blade 19 and a cam surface 28 engaging the face of the latter for turning the blade about its pivot pin 20 and varying the gap separating its other end from the trip bar. The flat lever has a pointed end 22 to align with scale markings on the front of the casing.

The trip mechanism B comprises a pair of metal blades, 1, 2 (FIG. 5) disposed substantially in line and pivotally supported at adjacent ends in knife edge bearings 3 in a bracket 3. The longer blade is provided at its other end with a contact 5 engageable with a fixed contact 9 disposed on a strap 29, on the other end of which is a terminal 30 of the coil circuit. The outer end of the other blade 2 is engageable by the hook formation 6. The blades are maintained in an overcenter position by a C-shaped spring 4 the ends of which are entered into slots in the blades, in known manner. A removable cover 42 for observing the trip mechanism is appropriately large in order to provide free access to the mechanism during the setting operation.

A slidable plunger 31, FIG. 5, extending through the trip chamber 18 is guided for longitudinal movement in the box against the action of a helical compression spring 32 coiled around its rear end 31 and has a formation 31 adapted for depressing a spring blade 33 to disengage a moving contact 34 from a fixed contact 34 on the bracket 3 to break the coil circuit of the starter. The plunger is adapted to be given a past turn so that a peripheral cam formation 31' thereon engages and lifts a back contact 10. This back contact is disposed on one end of a flexible blade 35, the other end of which is connected to the terminal 36 of a signal circuit.

In operation a normal balanced overload causes the bimetals to flex uniformly and cause their impingement on the plate 8 to move it to the right and, due to the fact that it is coupled to the plate 7 by the bellcrank 6, the plate 7 likewise moves to the right. This causes an extension 7 on this plate to abut against the ambient blade 19. This bar is arrested but the other 8 continues its movement to produce turning of the link 6 about its lower pivot 6, thereby causing the hook 6 thereon to actuate the mechanism. With single phasing the operation takes place in known manner as follows. Assuming open phase or single phasing at start with no current in the center pole, the outer bimetals deflect rapidly on heavy current, but the center bimetal 15 holds back the lower trip bar 7, while bar 8 moves rightwards. The bellcrank 6 pivots about 6" to actuate the trip mechanism.

With single phasing during running, the operation, again in known manner, is as follows. Assuming current ceases on the center pole, the center bimetal cools and moves leftwards relatively to the outer bimetals 15 taking with it the bar 7 to cause the bellcrank 6 and hook 6 to pivot about 6 to actuate the trip mechanism B.

The action of tripping effects the snapover of the moving contact from a fixed contact 9 to a contact 10 which is adjustable to vary the gap between them, to provide, in known manner, self-resetting or hand-resetting.

The support 3 comprises an L-shaped current-carrying bracket 3" which is adjustable so that the blades, with the C- spring are movable in their plane, in order to vary the position of engagement of one blade 2 with the bellcrank lever 6. The bracket is secured in position by a screw 11 on its end being tightened against the casing 12 which is formed with an elongated slot 13 for receiving the stem of the screw.

A second screw 14 in the casing is operative on the bracket at the angle of its bend for adjusting it to move its notched or recessed arm 3 in the direction of its length, in order to ensure predetermined location of the notches 3" in relation to the contact 9.

Attached to fixed contacts in the trip chamber are terminals having extended legs to assist the location of parts in the molding, the fixed contact being adjustable for the purpose of changing from hand to automatic resetting. The setting for manual or automatic resetting is determined by the position of the back contact 10 as shown in FIG. 5. The switch is placed in the automatic reset position by depressing the plunger 31, turning it through 90", and allowing it to retum'under the action of the spring 32. The rotational movement in the depressed position causes a longitudinal shoulder or rib 31 thereon to be disposed on the other side of a projection or stop 36 on terminal 36. In the full line position of this contact, the blades 1, 2 are permitted to flex overcenter to such an extent that the contact 5 engages the contact 10. This position is maintained by the C-spring until the plunger is pressed manually inwardly-that is downwardly as in FIG. 5to cause the sloping surface 31 thereon to engage the blade 35. This in turn causes the contact on the end of this blade to abut the contact 5 and thereby press blades 1, 2 to flex overcenter to the position shown in full lines. Thus manual resetting is effected.

For automatic resetting the plunger having been depressed and turned, as previously described, the peripheral cam 31" thereon moves the contact leftwards into the chain line position. The cam 31" acts to retain the blade 35 and the contact 10 in the chain line position. Thus the movement of the blades 1 and 2 is so limited that they cannot flex overcenter due to the narrowed or restricted gap between the contacts 5 and 10. Therefore, as soon as the pressure of the hook 6 on the blade 2 is released the blades 1, 2 are automatically restored by the C-spring to the position shown in full lines.

Assembly of parts is preferably carried out in jigs foraccurately positioning the adjustable contacts. The improved arrangement avoids electrical joints and thereby provides greater efficiency.

The coil of the contactor is connected to a terminal which is connected by bracket 29 and the trip mechanism, bracket 3, contacts 34, 34" to terminal 43 to the supply.

In FIG. 8 the supply is connected to terminal 44 and current flows through bracket 44, strap 44", bimetal l5, welded connection 44, winding 16, bracket 45 to motor terminal 45. Alternatively connection may be made from another contactor through the terminal 46, instead of the supply 44, or to another contactor through the terminal 45 instead of the terminal 45. A signal, either audible or visual may be connected through the blade 35 to a terminal 36.

The trip circuit is from terminal 43, stop contact 34, 34", bracket 3, trip blades 1, 2, contacts .5, 9, bracket 29 to terminal 30.

Depression of the plunger 31 opens the circuit at 34 by the engagement of the cam portion 31 with the bent protuberance 33 on the blade 33. If overload causes the circuit to be broken by disengaging contact 9 from 5 the plunger may be depressed to reengage these contacts.

Factory adjustment of the switch is effected by a setscrew which is operative, as seen in FIG. 8 to adjust a U-shaped bracket 40 to move the blade 7 to cause adjustment of the bellcrank lever 6 in relation to the blade 2 of the overcenter switch. Factory adjustment can also be effected by the setscrews 41 and 14 and all these screws can be sealed after adjustment, by a sealing composition to prevent subsequent tampering with them.

Having thus described my invention, 1 claim:

1. Thermal overload mechanism for protecting three-phase motors against balanced sustained overloads in each phase and unbalanced overloads, said mechanism comprising a molded casing (12) formed with partitions (17) to provide four compartments, slots disposed in said partitions, a thermal bimetal member (15) mounted in three of said compartments, a quick make and break overcenter switch supported in the fourth of said compartments, a C-spring (4), said switch comprising a pair of switch blades (1, 2), adjacent ends of which are connected by said C-s ring, flat trip bars (7, 8) having apertures therein, said trip ars guidingly slidable in said slots, the ends of said bimetals protruding into said apertures, a bellcrank (6) disposed in said fourth compartment and pivotally connected to adjacent ends of said trip bars, an arm (6) of said bellcrank abutting against the first (2) of said switch blades, a strap (29) carried by a terminal (30) on said casing, a fixed contact (9) on said strap, a moving contact (5) disposed on the second (1) of said switch blades cooperating with said fixed contact, a flexing blade (35) carried by a second terminal (36) mounted on said casing, a third contact (10) mounted on said flexing blade cooperating with said moving contact and adjustable to two positions for varying the gap between said moving and said third contacts, a plunger (31) longitudinally slidable in said casing, its depression adjusting and manually resetting said third contact after a tripping operation, said plunger being rotatable in its depressed position for automatic resetting of said third contact after a tripping operation, and adjustable setscrews (14) for said switch and (40) for said bellcrank mounted in sidewalls of said casing in the vicinity of said switch and said bellcrank, respectively.

2. Thermal overload mechanism according to claim 1, including a flat metal blade (19) which provides ambient temperature compensation and is mounted between its ends on said casing, one end of said trip bar (7) being engageable with said blade, said blade having stop means (19) thereon for abutment against a wall of said casing for limiting movement of said blade.

3. Thermal overload mechanism according to claim 2, including a pivotal fiat adjusting lever (22) mounted externally on a sidewall of said casing and having a slot therein, a pivoted bracket (25) embracing a wall of said casing, a pin (24) disposed on said pivoted bracket, said pin riding in said slot, a guiding member (27) carried by said pivoted bracket, an elongated slot (26) disposed in said ambient blade 19), said guiding member entering said elongated slot, and a cam (28) disposed on said bracket and engaging the surface of said ambient blade for varying the gap between said ambient blade and said trip bar (7).

4. Thermal overload mechanism according to claim 1, in which a current-carrying bracket (3) having notches (3) thereon is mounted in said casing (12), the ends of said switch blades (1, 2) being mounted in said notches, said setscrew (14) mounted in a sidewall of said casing and operative on said bracket to adjust the position of said notches and the overcenter position of said blades (1, 2).

5. Thermal overload mechanism according to claim 4, wherein said bracket is L-shaped, a terminal screw (11) securing one end of said bracket to said casing, the other end (3) provided with said notches (3) for seating the inner ends of said switch blades, and said setscrew (14) mounted in said casing and abutting said bracket adjacent the junction of its said arms for moving said notches and adjusting the position of the inner ends of said blades relative to said fixed contact (9). 

1. Thermal overload mechanism for protecting three-phase motors against balanced sustained overloads in each phase and unbalanced overloads, said mechanism comprising a molded casing (12) formed with partitions (17) to provide four compartments, slots disposed in said partitions, a thermal bimetal member (15) mounted in three of said compartments, a quick make and break overcenter switch supported in the fourth of said compartments, a C-spring (4), said switch comprising a pair of switch blades (1, 2), adjacent ends of which are connected by said C-spring, flat trip bars (7, 8) having apertures therein, said trip bars guidingly slidable in said slots, the ends of said bimetals protruding into said apertures, a bellcrank (6) disposed in said fourth compartment and pivotally connected to adjacent ends of said trip bars, an arm (6a) of said bellcrank abutting against the first (2) of said switch blades, a strap (29) carried by a terminal (30) on said casing, a fixed contact (9) on said strap, a moving contact (5) disposed on the second (1) of said switch blades cooperating with said fixed contact, a flexing blade (35) carried by a second terminal (36) mounted on said casing, a third contact (10) mounted on said flexing blade cooperating with said moving contact and adjustable to two positions for varying the gap between said moving and said third contacts, a plunger (31) longitudinally slidable in said casing, its depression adjusting and manually resetting said third contact after a tripping operation, said plunger being rotatable in its depressed position for automatic resetting of said third contact after a tripping operation, and adjustable setscrews (14) for said switch and (40) for said bellcrank mounted in sidewalls of said casing in the vicinity of said switch and said bellcrank, respectively.
 2. Thermal overload mechanism according to claim 1, including a flat metal blade (19) which provides ambient temperature compensation and is mounted between its ends on said casing, one end of said trip bar (7) being engageable with said blade, said blade having stop means (19a) thereon for abutment against a wall of said casing for limiting movement of said blade.
 3. Thermal overload mechanism according to claim 2, including a pivotal flat adjusting lever (22) mounted externally on a sidewall of said casing and having a slot therein, a pivoted bracket (25) embracing a wall of said casing, a pin (24) disposed on said pivoted bracket, said pin riding in said slot, a guiding member (27) carried by said pivoted bracket, an elongated slot (26) disposed in said ambient blade (19), said guiding member entering said elongated slot, and a cam (28) disposed on said bracket and engaging the surface of said ambient blade for varying the gap between said ambient blade and said trip bar (7).
 4. Thermal overload mechanism aCcording to claim 1, in which a current-carrying bracket (3b) having notches (3a) thereon is mounted in said casing (12), the ends of said switch blades (1, 2) being mounted in said notches, said setscrew (14) mounted in a sidewall of said casing and operative on said bracket to adjust the position of said notches and the overcenter position of said blades (1, 2).
 5. Thermal overload mechanism according to claim 4, wherein said bracket is L-shaped, a terminal screw (11) securing one end of said bracket to said casing, the other end (3) provided with said notches (3a) for seating the inner ends of said switch blades, and said setscrew (14) mounted in said casing and abutting said bracket adjacent the junction of its said arms for moving said notches and adjusting the position of the inner ends of said blades relative to said fixed contact (9). 